Laser welding is known from prior public use. In this technique, a laser beam is focused onto the workpiece which is to be welded. Often, a process gas which has to meet a number of demands is fed to the weld point at the same time. The intention is, on the one hand, to protect the laser optics used from spatter and contamination and, on the other hand, to prevent or limit undesirable reactions between the environmental atmosphere and the weld area. Generally, the process gas is directed through a nozzle which is coaxial with respect to the laser beam, although under certain circumstances a second nozzle which is directed transversely with respect to the laser beam may be used instead or in addition.
In the prior art, inert gases are generally used as the process gas. Nitrogen and argon are gases which are available at low cost, but they do have the drawback that the laser beam interacts with the nitrogen molecules or the argon atoms so as to form a process gas plasma which is undesirable for many applications, since it reduces the welding efficiency. Therefore, process gases which contain approximately .gtoreq.30% helium in argon are often employed. Helium suppresses plasma formation in the process gas.